So-called dud detector devices have been developed for testing the hermetic vacuum seal on containers, particularly baby food jars. These containers typically have a raised safety button or convex dome which inverts itself into a concave configuration when there exists the normal partial vacuum within the container. If such vacuum is lost, the button returns to its unstressed convex shape. The resulting container with an insufficient vacuum is referred to by the food packing industry as a "dud." Devices have been developed to detect duds by subjecting entire cases of such filled food container to a pressure in excess of atmospheric. If any duds are present, the pressure causes the safety button to flip from a convex to a concave configuration, thereby emitting a distinctive click. The dud detector apparatus is designed to sense such a click provide an indication to the operator of the existence of a dud. The case can then be removed for further inspection.
It has been found that the sensitivity of the dud detecting apparatus is quite critical. If the dud detector is too sensitive, extraneous background noise may give a false dud indication. This results in the needless expenditure of time and money of rejecting good containers. If the sensitivity of the dud detecting apparatus is too low, some duds may not be detected. This prospect is totally unacceptable for food containers, especially baby food containers. Therefore, it is apparent that the sensitivity of such dud detector devices is critical. Apparatus to reproduce the noise made by the safety button when flipped, thus enabling these dud detectors to be standardized, is needed.